Beijing — This week's ethnic violence in Urumqi, the capital of China's far western Xinjiang region, rang a second warning bell for Beijing's policy toward minorities just 18 months after a similar outburst by Tibetans in March 2008.

There is little sign yet, though, that the Chinese government is prepared to loosen its iron grip either on Tibet or the restive Muslim Uighur people in Xinjiang, say experts on the two regions. That augurs further unrest, they warn. On Wednesday, President Hu Jintao cut short his visit to the Group of 8 summit to return home to tackle the crisis.

Chinese officials have blamed Sunday's riot in Urumqi, which left 156 people dead – apparently mostly ethnic Han Chinese – on Uighur exile leader Rabiya Kadeer. Last year they blamed the Dalai Lama for the violence in Lhasa.

"They are missing the main problem, which is the real concern among Uighurs about how they are treated by Chinese society," says James Millward, a Xinjiang expert at Georgetown University in Washington. "They are missing an opportunity to relieve the stresses that have arisen."

Both Uighurs and Tibetans formerly enjoyed autonomy, and resent an influx in Chinese migrants and influence over the last half century. Apparently to prevent a breakup similar to that of the multiethnic Soviet Union, some analysts say, Beijing clenched its fist in the early 1990s after years of relatively relaxed rule over ethnic minority areas in western China.

"The root cause of the trouble is the departure from China being a multiethnic empire to being a unitary nation state," argues Nicholas Bequelin, a Xinjiang scholar who works for Human Rights Watch in Hong Kong. "That began the endgame for minorities."

Uighur anger over this clampdown has long been simmering, making Sunday's violence surprising only for its scale, says Mr. Bequelin.

"The writing was on the wall and human rights groups have been warning about it," he says. "When a central state assimilates an indigenous territory very rapidly it creates tensions that lead to periodic blowback."

Han population now 40 percent of Xinjiang

Workers belonging to the Han Chinese majority (who make up 90 percent of China's population) have been pouring into the mostly Muslim Uighur region of Xinjiang, rich in oil and gas, for 60 years.

Pushed to move under Mao Zedong (China's ruler from 1949-76), and more recently pulled by economic incentives, the Han have gone from 6 percent to more than 40 percent of the autonomous region's population.

Tibet has experienced similar, if much-smaller-scale migration of Han Chinese.

The government's settlement policy is driven by security concerns, say foreign experts, and by a conviction in Beijing that Tibet and Xinjiang are integral parts of China.

That is not a view shared by local inhabitants, who "have competing identities that run counter to the way China tries to define them as Chinese minorities," says Elliot Sperling, a professor at Indiana University in Bloomington. [Editor's note:The original version misstated the name of the university.]

Security the 'guiding principle' of Beijing's policy

But with a rising Han population – and military garrisons – reinforcing frontier security, and security "the absolute guiding principle" of Beijing's policy toward minorities, says Wenran Jiang, who teaches at the University of Alberta in Canada, "there is no doubt ... that any means will be used to crush any aspirations to separatism."

That is bound to cause friction with "national groups fully conscious of having had states ... within living memory," warns Professor Sperling, a Tibet scholar. China enjoyed no authority before 1951 in areas of Tibet under the rule of the Dalai Lama, he points out, and Xinjiang was briefly the independent republic of East Turkestan between 1945 and 1949, when Mao's troops took over.

Minorities left out of economic development plan

The tensions have been worsened because although breakneck economic development has made Xinjiang richer, most of the benefits have gone to the Han, Uighurs complain. Tibetans harbor similar resentments, says Robbie Barnett, a Tibet expert at Columbia University in New York.

"The focus was all on GDP growth, with no capacity building" for less educated and less skilled rural Tibetans and Uighurs, he points out. "It was one-size-fits-all development."

"The undeveloped Xinjiang minority group areas were not included in the development plan" that built oil and gas wells with imported labor and planted cotton farms tended by demobilized Chinese soldiers, wrote Ilihamu Tuheti, a Uighur professor at Beijing's Nationalities University, on his blog.

Unusual crackdown on 'state security' offenses, religion

After Beijing began cracking down in the 1990s, officials began demonizing the Dalai Lama as a "splittist." Uighurs found themselves unable to voice the slightest complaint without being branded traitors. During the first years of this decade, according to Bequelin, nearly 10 percent of prisoners in Xinjiang were serving sentences for state security crimes. The corresponding ratio for the whole of China was 0.005 percent.

In both Tibet and Xinjiang, the authorities have cracked down on religious practice in a manner unheard of elsewhere in China. No government employee in either region is allowed to attend religious services, for example, and no young men under 18 are allowed to attend a mosque in Xinjiang.

"The Uighurs [ethnically related to other peoples of Central Asia] have a Turkic identity that the Chinese are trying to smother because it has transnational elements to it" that could threaten Chinese security, says Sperling.

Debate in Communist party about tactics, policy?

He is pessimistic about the Uighurs' cultural future. The Chinese government, he says, "believes that Sinicization is inevitable in the tide of history. But it is not going to happen without friction because it involves marginalizing people in their own area."

The way in which officials instantly blamed exiles for instigating Sunday's violence, he adds, "does not suggest much soul searching" about government policy toward minorities. Nor, 18 months on, has Mr. Barnett seen any signs of changed policy in Tibet.

"The Chinese have time, power, resources – everything is on their side," agrees Bequelin.

Others see signs of a debate within the ruling Communist party. "The first thing the authorities need to do is to actually acknowledge the problem" says Professor Jiang. He believes that "more thoughtful" leaders will seek a "more sophisticated" response to Sunday's unrest than a further crackdown.

That does not yet seem to be the case. "If the minority groups in Xinjiang are poor and backward, it is difficult to maintain peace and stability there" wrote Professor Tuheti prophetically on his blog last August.